Polyethylene Unsaturation

Much useful information regarding the types of unsaturation present in polyethylene can be gained by IR spectroscopy. Polyethylenes can contain various types of 

In branched polyethylene, most of the unsaturation is of the external vinylidene type, whereas trans olefinic end groups and terminal vinyl groups are relatively low in concentration. In linear polyethylene, most of the unsaturation is terminal vinyl with relatively small amounts of external vinylidene and trans olefinic end groups. 

The electron irradiation of linear and branched polyethylenes causes several molecular rearrangements in the polymer structure [59]. In addition to the significant changes in the type and distribution of unsaturated groups, IR comparison of the radiation-induced chemical changes that occur in air and in a vacuum showed that oxygen has a marked influence on the structural rearrangements that occur on irradiation. 

Irradiation in a vacuum produces a significant decrease in methyl (-CH3) content (1373 cm ) (7.28 pm), whereas in the bombardment in air there appears to be only a negligible decrease in -CHj (if any). 

Comparison of the 720-730 cm (13.89-13.70 pm) doublet shows that only the 720 cm (13.89 pm) component in the air-irradiated sample remains in the spectrum of the vacuum samples, whereas there is only a slight decrease of the 730 cm i (13.69 pm) component in the air-irradiated samples. Additional evidence of structural changes is shown in the spectra of the air-irradiated sample. Here -OH and C=0 hands appear, and there is a general depression of the spectrum background from 1300 cm to 900 cm (7.69-11.11 pm). 

Much useful information regarding the types of unsaturation present in polyethylene can be gained by the application of IR spectroscopy. Polyethylenes can contain various types of unsaturation which are of great importance from the microstructural point of view. These include, external vinylidene, terminal vinyl and internal cis and trans unsaturation. 

Unsaturation in low-density polyethylene has been estimated to 0.003 C = C/10 C atoms by compensating with brominated polymer of the same thickness [60]. 

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PS PSF PSU PTFE PU PUR PVA PVAL PVB PVC PVCA PVDA PVDC PVDF PVF PVOH SAN SB SBC SBR SMA SMC TA TDI TEFE TPA UF ULDPE UP UR VLDPE ZNC Polystyrene Polysulfone (also PSU) Polysulfone (also PSF) Polytetrafluoroethylene Polyurethane Polyurethane Poly(vinyl acetate) Poly(vinyl alcohol) poly(vinyl butyrate) Poly(vinyl chloride) Poly(vinyl chloride-acetate) Poly(vinylidene acetate) Poly(vinylidene chloride) Poly(vinylidene fluoride) Poly(vinyl fluoride) Poly(vinyl alcohol) Styrene-acrylonitrile copolymer Styrene-butadiene copolymer Styrene block copolymer Styrene butadiene rubber Styrene-maleic anhydride (also SMC) Styrene-maleic anhydride (also SMA) Terephthalic acid (also TPA) Toluene diisocyanate Ethylene-tetrafluoroethylene copolymer Terephthalic acid (also TA) Urea formaldehyde Ultralow-density polyethylene Unsaturated polyester resin Urethane Very low-density polyethylene Ziegler-Natta catalyst... 

As an option in both associative and conventional ASTs, some minor amounts of other water-soluble or water-insoluble monomers may be included, as well as minor amounts of polyethylenically unsaturated monomers, to provide a low degree of cross-linking. The nuances of classification by chemical architecture are elaborated on further in this chapter under the section entitled AST Thickening Mechanisms , subsection Associative or Nonassociative ... 

The commodity thermosets of urea, melamine, and phenolics account for about one-third of building and construction industries resin consumption. Most of this is used for resin-bonded woods such as plywood, particle board, and oriented strand board. High-density polyethylene (HDPE), used primarily for rigid piping, accounts for about 5% of consumption. Other significant resins, accounting for 3-5% of total consumption, include other polyethylenes, unsaturated polyester, and polystyrene. 

Organic peroxides are used in the polymer industry as thermal sources of free radicals. They are used primarily to initiate the polymerisation and copolymerisation of vinyl and diene monomers, eg, ethylene, vinyl chloride, styrene, acryUc acid and esters, methacrylic acid and esters, vinyl acetate, acrylonitrile, and butadiene (see Initiators). They ate also used to cute or cross-link resins, eg, unsaturated polyester—styrene blends, thermoplastics such as polyethylene, elastomers such as ethylene—propylene copolymers and terpolymers and ethylene—vinyl acetate copolymer, and mbbets such as siUcone mbbet and styrene-butadiene mbbet. 

The use of TAG as a curing agent continues to grow for polyolefins and olefin copolymer plastics and mbbers. Examples include polyethylene (109), chlorosulfonated polyethylene (110), polypropylene (111), ethylene—vinyl acetate (112), ethylene—propylene copolymer (113), acrylonitrile copolymers (114), and methylstyrene polymers (115). In ethylene—propylene copolymer mbber compositions. TAG has been used for injection molding of fenders (116). Unsaturated elastomers, such as EPDM, cross link with TAG by hydrogen abstraction and addition to double bonds in the presence of peroxyketal catalysts (117) (see Elastol rs, synthetic). 

Sulfurized olefins (S2CI2 plus isobutene) are further reacted with S and Na2S to give products useful as extreme pressure lubricant additives (144,145). The reaction of unsaturated natural oils with sulfur monochloride gives resinous products known as Factice, which are useful as art-gum erasers and mbber additives (146,147). The addition reaction of sulfur monochloride with unsaturated polymers, eg, natural mbber, produces cross-links and thus serves as a means for vulcanizing mbber at moderate temperatures. The photochemical cross-linking of polyethylene has also been reported (148). 

Ozonc-rcsjstant elastomers which have no unsaturation are an exceUent choice when their physical properties suit the appHcation, for example, polyacrylates, polysulfides, siHcones, polyesters, and chlorosulfonated polyethylene (38). Such polymers are also used where high ozone concentrations are encountered. Elastomers with pendant, but not backbone, unsaturation are likewise ozone-resistant. Elastomers of this type are the ethylene—propylene—diene (EPDM) mbbers, which possess a weathering resistance that is not dependent on environmentally sensitive stabilizers. Other elastomers, such as butyl mbber (HR) with low double-bond content, are fairly resistant to ozone. As unsaturation increases, ozone resistance decreases. Chloroprene mbber (CR) is also quite ozone-resistant. 

Plasticizers and Processing Aids. Petroleum-based oils are commonly used as plasticizers. Compound viscosity is reduced, and mixing, processing, and low temperature properties are improved. Air permeabihty is increased by adding extender oils. Plasticizers are selected for their compatibihty and low temperature properties. Butyl mbber has a solubihty parameter of ca 15.3 (f /cm ) [7.5 (cal/cm ) ], similar to paraffinic and naphthenic oils. Polybutenes, paraffin waxes, and low mol wt polyethylene can also be used as plasticizers (qv). Alkyl adipates and sebacates reduce the glass-transition temperature and improve low temperature properties. Process aids, eg, mineral mbber and Stmktol 40 ms, improve filler dispersion and cured adhesion to high unsaturated mbber substrates. 

Polybutenes enjoy extensive use as adhesives, caulks, sealants, and glaring compounds. They are used as plasticizers in mbber formulations with butyl mbber, SBR, and natural mbber. In linear low density polyethylene (LLDPE) blends they induce cling to stretch-wrap films. Polybutenes when modified at their unsaturated end groups with polar fiinctionahty are widely employed in lubricants as dispersants. Blends of polybutene with polyolefins produce semisoHd gels that can be used as potting and electrical cable filling materials. 

This is a material produced from the impregnation of glass fibre-mat (fibreglass, which is in the form of dry sheet, is commonly known as chopped stranded mat (CSM)) or rovings, with a liquid and unsaturated polyester resin, which thickens chemically to a dry sheet form. The total mix is sandwiched between polyethylene films and then roller-pressed to impregnate and consolidate it. 

Their physieal properties are essentially those of the alkanes. It is the unsaturated linkages that dominate the ehemistry and the main reaetion is one of addition (e.g. hydrogen, halogen, and hydrogen halides) aeross the double bond to produee saturated eompounds. This reaetivity is utilized in the manufaeture of long-ehain polymers, e.g. polyethylene and polypropylene. 

Ethylene, a simple, unsaturated organic molecule, is made into translucent, inexpensive, waxy polyethylenes at high pressures. When polyethylenes are applied to substrates, the resulting film is resilient and resistant to acids and oxidizers,... 

Polyethylene glycol 400 cysteine adducts of a-, -unsaturated aldehydes as dansyl hydrazones stabilization and enhancement dipping solution, 25% in chloroform [268]... 

Addition polymers are formed by the reaction of the monomeric units without the elimination of atoms. The monomer is usually an unsaturated organic compound such as ethylene, H2C=CHs, which in the presence of a suitable catalyst will undergo an addition reaction to form a long chain molecule such as polyethylene. A general equation for the first stage of such a process is... 

Polyolefins Plastics such as polyethylene (PE), polypropylene (PP), and polybutylene (PB) that are derived from unsaturated hydrocarbons (also called olefins). 

Compared with tar, which has a relatively short lifetime in the marine environment, the residence times of plastic, glass and non-corrodible metallic debris are indefinite. Most plastic articles are fabricated from polyethylene, polystyrene or polyvinyl chloride. With molecular weights ranging to over 500,000, the only chemical reactivity of these polymers is derived from any residual unsaturation and, therefore, they are essentially inert chemically and photochemically. Further, since indigenous microflora lack the enzyme systems necessary to degrade most of these polymers, articles manufactured from them are highly resistant or virtually immune to biodegradation. That is, the properties that render plastics so durable... 

Figure 1 Evolution as a function of the number of unit cells (N) of the longitudinal polarizability per unit cell, AoIl(N) = l(N) - 0[l(N-1) for prototypes of saturated (polyethylene) and unsaturated (polyacetylene) polymers.

The effect of incorporating p-hydroxybenzoic acid (I) into the structures of various unsaturated polyesters synthesised from polyethylene terephthalate (PET) waste depolymerised by glycolysis at three different diethylene glycol (DEG) ratios with Mn acetate as transesterification catalyst, was studied. Copolyesters of PET modified using various I mole ratios showed excellent mechanical and chemical properties because of their liquid crystalline behaviour. The oligoesters obtained from the twelve modified unsaturated polyesters (MUP) were reacted with I and maleic anhydride, with variation of the I ratio with a view to determining the effect on mechanical... 

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